A known load sensor is disclosed, for example, in JP2009-128106A which is hereinafter referred to as Reference 1. The load sensor disclosed in Reference 1 includes a strain body to which a strain gauge is attached. A center portion of the strain body is fixed to a first member (a frame). Opposed end portions of the strain body are fixed to a second member (an upper rail). In a case where a load in an up-down direction is applied to the first member, the strain gauge is configured to be elastically deformed. The load sensor electrically detects the aforementioned load based on changes in electric resistance of the strain gauge which occurs in association with the elastic deformation of the strain body.
According to Reference 1, in a case where a large load in the up-down direction is applied to the first member at a time of vehicle collision, for example, the strain body may be plastically deformed beyond its elastic limit. In this case, the strain body is unable to return to its original form, which may lead to deterioration of load detection accuracy.
A need thus exists for a load sensor which is not susceptible to the drawback mentioned above.